This disclosure relates to a fuel fluidizing nozzle assembly for a fluidized bed reactor.
The use of fluidized bed reactors for the incineration of waste fuels, such as municipal refuse and high alkali fuels is generally known and involves the burning of these fuels with air while fluidizing it in a fluidized bed. The upper section of the reactor is typically equipped with a waste fuel feeding unit, and the waste fuel is burned while it is fluidized by primary air, which is blown through nozzle assemblies in a lower section of the reactor body.
The fuels are generally of low calorie content and contain a high percentage of tramp material that does not burn. As the fuels are fed to the fluidized bed, the volatile organic compounds are burned and coarse material, such as tramp material, spent bed make-up material, and ash, remain in the fluidized bed. Therefore, a fluidized bed reactor for the incineration of waste and high alkali fuels is typically equipped with a means in the lower section of the reactor body which is designed to provide fluidizing air to the fluidized bed while allowing coarse material to be removed from the reactor.
One example of a means for removing coarse material is depicted in FIG. 1, which is a top plan view of an open-floor grate assembly 10 disposed in the lower portion of a fluidized bed reactor 12. The grate assembly 10 includes a number of parallel, spaced apart air ducts 14 (also known as air pipes or bars, sparge pipes, and hydro tubes) extending side-by-side in a substantially horizontal plane. Air nozzle assemblies 16 are attached to the air ducts 14 for supplying fluidizing air from within the air ducts 14 into the fluidized bed of fuel, which is located above the grate assembly. As the organic compounds are decomposed and burned within the fluidized bed, the coarse material descends downwardly through spaces 18 between the air ducts 14. The coarse material is then discharged to external equipment and a portion of the bed make-up material may be separated from the coarse material and returned to the fluidized bed. Examples of such grate assemblies are described in U.S. Pat. No. 5,966,839 and U.S. Pat. No. 5,425,331, the contents of which are incorporated by reference herein in their entirety.
FIG. 2 depicts a cross-sectional elevation view of a portion of an air duct 14 including nozzle assemblies 16. Each nozzle assembly 16 is formed from a hollow tube 30 having an end cap 33 welded thereon and a plurality of nozzle holes 34 disposed therein proximate the end cap 33. The nozzle assemblies 16 are attached through an upper wall 32 of the air duct 14, and air from the air duct 14 passes through the hollow tube 30, and out the nozzle holes 34 into the fluidized bed of fuel. The air duct 14 may include pipes 36 through which a cooling medium, such as water, flows.
While such an arrangement works well when the nozzle assemblies 16 are newly installed, over time the nozzle holes 34, which are typically ¼ inch in diameter or less, will become plugged due to the presence of alkali materials. More specifically, alkali material gets into the nozzle assembly due to gas recirculation to the reactor and solids back flow from the bed. These alkalis cause a sticky build up on the nozzle assemblies, particularly at the nozzle holes and at any bends in the tube, which result in plugging of the nozzle assemblies. The quick plugging results in much less than the desired operating time between reactor outages for maintenance. Furthermore, repair of the nozzle assemblies typically requires cutting the top portion of the nozzle assembly, and welding a new top portion in its place, which is a time-consuming process that can extend the duration of reactor outages.
Thus, there is a need for a nozzle assembly for use in a grate assembly of a fluidized bed reactor that reduces the likelihood of plugging and, therefore, reduces the frequency of reactor outages. Furthermore, there is a need for an easily replaceable nozzle assembly to help reduce the duration of such outages.